1. Field of the Invention
The present invention relates generally to the area of food and beverage apparatus and, more particularly, to a scroll and screen centrifuge having self-cleaning components.
2. Description of Related Art
It is well known to use a scroll and screen centrifuge to separate a crystalline, a granular or a fibrous product from a liquid in which the crystalline, granular or fibrous product is carried. Scroll and screen centrifuges are typically used with a continuous process in which a combined liquid and solid material is continuously fed into and continuously discharged from the centrifuge. The continuous process is distinguished from a batch process in which a batch of liquid and solid material is fed into the centrifuge; and the liquid and solid materials are separated. The centrifuge is stopped, and the separated materials are removed before another batch is loaded into the centrifuge. Both the continuous and batch separation processes are also considered to dry the solid material. The separation process is used in a wide range of applications including the production of soap powders, coal, gypsum, plastic granules, potash, salt, etc.
In a typical scroll and screen centrifuge, a frustoconical basket and scroll assembly is mounted for rotation within a housing. Within the basket and scroll assembly, a frustoconical scroll member having a tubular side wall with outwardly projecting helical screw flights is mounted for rotation within an independently rotating frustoconical basket member; and the screen is mounted on a circumferential surface of the basket member. The scroll member rotates at a slightly greater velocity than the basket member so that the helical screw flights on the scroll member pass in close proximity to and over the screen. The helical length of the screw flights varies from a fraction of a revolution to several revolutions around the scroll member. A liquid with solids therein is fed into a closed, rearward portion of the frustoconical basket and scroll assembly. The rotation of the basket and scroll assembly creates centrifugal forces which cause the liquid to pass through openings in the screen thereby separating the liquid from the solids. The rotational velocity difference between the scroll member and screen causes the screw flights to push the solid material across the screen from the smaller, closed, rear end of the basket and scroll assembly to its larger, open, forward end from which the solid material is discharged. The processing time of the material in the centrifuge is controlled by the number and pitch of the helical screw flights on the scroll member and the difference in angular velocities between the basket and scroll members. The solid material is discharged as particles into a discharge opening and gravity and turbulence caused by the rotating basket and scroll assembly moves the solid particles through the discharge opening to other equipment or a collection unit.
Such scroll and screen centrifuge designs have a disadvantage of having limited application in the food processing industry due to the special machinery requirements for processing food and dairy products. For example, machinery used in processing dairy products should not have metal to metal contacts exposed to the dairy products. All areas of the machine that are exposed to the dairy products including seals, should be washable. There should be no places where product can collect thereby allowing bacteria to grow. Consequently, the superior performance and efficiency of a scroll and screen centrifuge for solid/liquid separation has not been widely used in the dairy industry.